Redundancy

WinCC OA redundancy

Both drivers (on the active and the passive side) establish all configured connections to the MQTT broker. Writing data is only possible on the active side. If the passive driver also shall activate subscriptions use the config entry onlyActiveSubscribes.

Redundant connection

In case of a redundant connection the driver establishes two connections to the same MQTT broker. The redundant connection is configured via data point element _MQTTConnection.Config.ReduAddress. When receiving value notifications via both connections, the driver rejects the second one (determined using current or received timestamp) to avoid sending value duplicates to the Event manager. Values to the broker are only written via one connection (the active one).

Each connection observes its connection state. In case of a connection loss, the automatic reconnect functionality switches the active connection and it is periodically tried to reconnect the other one.